Perfluorocarbons are generally non-toxic, safe, volatile, non-reactive, compounds, which are environmentally benign, especially when released on limited quantities. The ambient background concentrations of the five perfluorocarbons routinely used as tracers (PFTs) are in the range of parts per 1015 of air. The PFTs, by virtue of their high vapor pressure, provide the unique ability to permeate closed doors and windows, containers and luggage. On the other hand, PFTs can be optically or physically detected, and are impervious to electronic interference and other problems inherent with other tagging technologies. Once a location reaches steady state, the actively emitting tagged item will provide vapor traces that are detectable in the vicinity of the item (even temporarily following removal of the tagged item). By extending the detectable life of the perfluorocarbon tag materials, PFTs have been previously known to provide a unique tool for law enforcement in numerous applications including marking and tracking of currency and other non-invasive inspection scenarios when seeking various items of contraband under surveillance.
PFT technology has already been developed and utilized in various applications including: (1) detection of leaks in underground storage tanks; (2) detection of leaks in high-pressure, oil-filled electric transmission lines; (3) atmospheric tracing and air pollution dispersion studies; (4) building ventilation studies; (5) detection of tagged explosives (blasting caps) in airline luggage; (6) detection of leaks in natural gas pipelines; and (7) currency tracking in cases of kidnappings. It has also been proposed for early warning fire detection systems.
U.S. Pat. Nos. 3,991,680 and 4,256,038, expressly incorporated herein by reference, relate to methods of detecting small bombs to provide security against terrorist activities which can cause the destruction of civil aircraft in flight or detonate explosives in places where large groups of people congregate. These methods involve the tagging of explosive materials such as blasting caps with a so-called “vapor taggant” which can be “sniffed” and detected by suitable equipment. The vapor taggant disclosed in U.S. Pat. No. 3,991,680 is sulfur hexafluoride (SF.sub.6) absorbed in a fluoro-polymer. The vapor taggant disclosed in U.S. Pat. No. 4,256,038 is includes one or a plurality of the following compositions: perfluorocycloalkanes such as perfluorodimethylcyclobutane (PDCB), perfuoromethylcyclohexane (PMCH), and perfluorodimethylcyclohexane (PDCH); perfluoroaromatics such as hexafluorobenzene (HFB), octafluorotoluene (OFT), decafluorobiphenyl (DFBP), decafluoroxylene (DFX), octafluoronaphthalene (OFN), and pentafluoropyridene (PFP), perfluoroalkanes such as perfluorohexane (PFH), perfluoropentane (PFPT), and perfluorooctane (PFO), and perefluorocycloalkenes such as decafluorocyclohexene (DFCH) and octafluorocyclopentene (OFCP). Examples of elastomers which are compatible with several of these taggants are copolymers of vinylidene fluoride and hexafluoropropylene. The following PFT compositions are also particularly useful as taggants: pf-methylcyclopentane (PMCP); pf-1,2-dimethylcyclohexane (o-PDCH1); pf-1,3-dimethylcyclohexane (m-PDCH1); pf-1,4-dimethylcyclohexane (p-PDCH1), pf-trimethylcyclohexanes (PTCH), perfluorodecalin (Octadecafluorodecahydonaphthalene, PFD, CAS 306-94-5), and perfluoro(methyl)decalin (PFMD, CAS 306-92-3). These compositions may be combined, as desired, to form a specific “cocktail”; i.e., a taggant that can be selectively detected and discriminated with respect to other taggants.
As used herein. PFT's are intended to refer to a class of chemical entities which have at least one —CF2—CF2— portion, or otherwise has an optical spectral characteristics corresponding to those resulting from the highly electronegative fluorine substituents, such that the compound is spectrographically distinguishable at very low concentrations, i.e., less than ppm level, and preferably less than ppb levels, from environmentally common substances. In some cases, a non-perfluorinated fluorocarbons may also be suitable for use, and to the extent that these have similar or advantageous remote detection characteristics, have low toxicity, good environmental stability (but perhaps less so than the perfluorocarbons, to reduce detrimental long-term environmental persistence and global warming potential), and appropriate volatility and dispersion in air, these may also be included with the scope of PFTs as encompassed herein.
Taggant use involves the detection of gaseous vapors (in minor tracer quantities) that are emitted over time. As there are a plurality of separate usable tracers in the PFT family, each with its own “fingerprint”, the PFTs can be combined in a range of combinations and concentrations, yielding thousands of discrete “signatures”. This allows discrimination between various compositions and enables the individual detection of multiple products, or the tracking of individually tagged products to provide exact identification and location.
The PFT technology is the most sensitive of all tracer technologies because the ambient background levels of the routinely used PFTs are extremely low (in the range of parts per quadrillion-ppq), and PFTs can be measured down to those levels.
It is the physical and chemical inertness of the PFTs that not only prevents their loss in the atmosphere, but also helps in their separation and analysis from less stable interfering compounds and makes them biologically inactive; and thus safe to use. Their limited industrial use not only results in low ambient background concentration, but also limits the possibility of numerous higher local concentrations that might confuse detection capability.
John H. Heiser and Arthur J. Sedlacek, “Using LIDAR to Measure Perfluorocarbon Tracers for the Verification and Monitoring of Cap and Cover Systems”, Brookhaven National Laboratory (2005), www.ecd.bnl.gov/pubs/BNL-75583-2006-JA.pdf, expressly incorporated herein by reference, teaches the use of LIDAR to detect PMCH, a perfluorocarbon.
Mason K Harrup, “Use of Custom Polyphosphazenes as Tunable Matrices for the Controlled Release of PFTs” (White Paper), expressly incorporated herein by reference, discloses a “tuned” polyphosphazene matrix, having a balance of perfluoronated pendant groups designed to hold the PFT tightly, providing slow release, and polar pendant groups designed to be incompatible with the PFT, providing fast release, to thereby control the observed PFT release rate.
U.S. Pat. No. 6,025,200, expressly incorporated herein by reference, relates to remote optical detection of PFTs. According to U.S. Pat. No. 6,025,200, cyclodextrins, liposomes, and synthetic polymer systems can be used in the development of encapsulated PFTs. As a group, these technologies provide a menu of tracer devices which can be tailored to meet a specific need. Cyclodextrin-PFT complexes can be formulated as a dispersion, true solution, or as solid crystalline powder. The cyclodextrin-PFT complexes can be made in water or mixed solvent systems and isolated as a free-flowing powder by spray drying or filtration from the mother liquor. The complex can be formulated in its mother liquor or used as a true solution or dispersion.
U.S. Pat. No. 6,214,624, expressly incorporated herein by reference discloses the use of PFTs to track hydrocarbon liquids. U.S. Pat. No. 5,409,839, expressly incorporated herein by reference, is entitled and describes a method for the tagging and detection of drugs, crops, chemical compounds and currency with perfluorocarbon tracers. U.S. Pat. No. 6,617,591, expressly incorporated herein by reference, relates to remote detection of explosives, for example, buried mines. See also, U.S. Pat. Nos. 4,520,109, 5,173,298, 5,362,568, 5,585,112, 5,853,752, 6,071,495, and 6,196,056, expressly incorporated herein by reference.